Annex 13 Complementary information to source category 1e Sewage Sludge Incineration
Overview of recent revisions
No revisions were made to emission factors in this source category. Additional guidance has been introduced on classifying sources within this category, estimating activity rates, and on data quality aspects.
Derivation of emission factors
Release to Air
Releases to air represent the most important vector for Class 1 and Class 2 sewage sludge incinerators. The default emission factor for class 1 was determined based on an average emission concentration of 4 ng TEQ/Nm³ (at 11% O2) and a specific flue gas volume flow rate of about 12,500 Nm³/t of sewage sludge burned based on a Belgian study as well as value of 77 ng TEQ/kg reported from the UK for a multiple hearth furnace with ESP. For Class 2, the emission factor is based on data from The Netherlands for fluidized bed plants with scrubbers and ESP. Class 3 is for fluidized bed plants with optimized air pollution control systems consistently meeting the emission limits equivalent to 0.1 ng TEQ/Nm³ (at 11% O2) (from Canadian, German and Swiss measurements) (LUA 1997, IFEU 1998, Environment Canada 1999).
PCB emission factors to air have been derived in a measurement campaign in France (Delepine et al. 2011). For class 3, high technology sewage sludge incinerators, emission factors in the range of 0.001-0.004 µg TEQ/ ton of sewage sludge are calculated for dioxin-like PCBs, and between 12 – 28 µg/t of sewage sludge incinerated for indicator PCBs.
Release to Water
PCDD/PCDF concentrations in scrubber effluent from sewage sludge incinerators are not available. However, when wastewater from wet scrubbers is treated and then reintroduced to the incinerator, no PCDD/PCDF are released from the incineration plant to water. Where plants use wet scrubbers or simple water quench is applied to cool down the off-gases or to quench grate ash this should be noted as well as the treatment and fate of the effluents. The European inventory reports concentrations between 1.2 and 6.5 pg TEQ/L in scrubber effluents from sewage sludge incinerators (EC 1999a).
Release to Land
No release to land is expected unless untreated residue is directly placed onto or mixed with soil.
Release in Products
The process has no product, thus no release to product occurs.
Release in Residues
UK testing of multiple hearth furnaces showed PCDD/PCDF in the grate ash at concentrations of 39 ng TEQ/kg and 470 ng TEQ/kg in fly ash from the ESP (Dyke et al. 1997). Rates of ash production were 430 kg per ton of grate ash and 13 kg per ton of ESP ash for the multiple hearth plant. Levels in ash (all the ash was collected in the ESP) from fluidized bed combustion were much lower (<1 ng TEQ/kg). 373 kg of ESP ash was produced per ton of sludge combusted in the fluidized bed. Class 1 releases to residues (combined) are therefore 23 µg TEQ/ton of waste. Class 2 releases are 0.5 µg TEQ/ton of waste. Class 3 releases are estimated the same as class 2.